Flame ignition system for cutting machines

ABSTRACT

A method of establishing a self-sustaining high-velocity oxyfuel preheat gas flame comprising pulsating the flow of the preheat gas while igniting same, at a rate such that the average gas velocity is rendered nearly equal to the rate of flame propagation.

United States Patent inventors George l-LTikijian {56] References Cited Maplewwd= UNITED STATES PATENTS AlexanderJordamCraniord,both oi,N.J. 1 376 828 5/1921 penis 239/413 QI J- 23:52: 1.912,243 5/1933 Andrews I A 431/1 d N 133971 2,480,626 8/1949 Bodine,Jr 60/208 2929,210 3/1960 Howes v 1 60/39.82P Assgnee Unmncarbmecmpmm 3,171,465 3/1965 Rydberg. 431 1 New 3,194,295 7/1965 Marchaletal 431 1 Primary Examiner-Frederick L. Matteson Assistant Examiner- Robert A. Dua

FLAME IGNITION SYSTEM FOR CUTTING Att0rneys Paul A. R086, Thomas I. OBrien, Dominic J.

MACHINES Terminello and Eugene Lieberstein 2 Claims, 3 Drawing Figs.

U.S. Cl 431/1, ABSTRACT: A method of establishing a self-sustaining high- 60/39.82 P. 239/413, 266/23 R velocity oxyfuel preheat gas flame comprising pulsating the Int. Cl F23c 3/02 flow of the preheat gas while igniting same, at a rate such that Field of Search 431/1, 6; the average gas velocity is rendered nearly equal to the rate of 60/39.82 P; 239/413; 266/23 R flame propagation.

FUEL 04s 7 COMBUSTION CUTTING 6A5 j?- supeom'me GAS IGNITION GAS SPARK SIGNAL PILOT IGNITEQ PATENTED JIIII 3 IIIII v 3592-57 3 SHEET 1 0F 2 FUEL GAS 78 ,I COMBUSTION SUPPORTING GAs 24 IGNITION I A GAS V SPARK SIGNAL PILOT IGNITER TIMING DIAGRAM Complete Cycle Torch Operahng Cycle I F! l lgmhon PerIod I Energizahon of I Pret1e)af Valves Preh af Time I Period (d) Guthng TIme Period @1 INVENTORS 42912 ALEXANDER JORDAN GEORGE H. IKIJIAN ATTORN EY FLAME IGNITION SYSTEM FOR CUTTING MACHINES This invention relates to thermotreating operations and more particularly to a method of establishing a self-sustaining high-velocity oxyfuel preheat gas flame.

In thermotreating processes such as metal piercing, cutting, etc. heat is applied to a workpiece by means of an oxyfuel gas flame. Initially, fuel gas and a combustion-supporting gas is combined in a predetermined proportion and directed against the surface of the workpiece. When ignited the mixed gas forms the preheat flame which raises the temperature of the workpiece to its sweat" temperature for performing the cutting or piercing operation. For fuel gases such as natural gas or propanes it is desirable to have a high exit preheat gas velocity. However, with high gas velocity the flame has a tendency to blow itself out. It has heretofore been difficult to establish a high-velocity preheat flame which would sustain itself after removing the pilot igniter. For purposes of the present disclosure high gas velocity is defined as being at least 100 f.p.s. (feet per second) or greater.

It is therefore the principal object of the present invention to provide a method of establishing a self-sustaining highvelocity oxyfuel preheat gas flame.

Other objects, features and advantages of the present invention will be apparent from the following detailed description.

It has been discovered in accordance with the present invention that a self-sustaining preheat gas flame may be established by pulsating the flow of preheat gas during the ignition period. The tendency of the flame to extinguish itself is believed to result from a flame propagation rate which is lower than that of the gas exit velocity. In accordance with this theory a self-sustaining flame will be established by pulsating the preheat gas at a rate such that the average gas velocity at exit is rendered nearly equal to the rate of flame propagation.

In the drawings:

FIG. 1 is a front plan view of an oxyfuel gas cutting torch or blowpipe and a spark igniter;

FIG. 2 is a timing diagram of a complete cycle of operation;

FIG. 3 is a schematic block diagram of the preferred system for pulsating the flow of preheat gas in accordance with the present invention.

Referring now to FIG. 1 in which an oxyfuel gas cutting torch T sometimes referred to as a cutting blowpipe is shown diagrammatically having a nozzle portion N through which the preheat gas and cutting gas is discharged. The combustionsupporting gas which in most cases is oxygen is supplied to gas conduit 12 through a solenoid valve 18 while the fuel gas to be proportionally mixed with said combustion-supporting gas is fed to gas conduit 14 through a solenoid valve 20. The mixing of the fuel gas, which may be for example either natural gas, propane, methane, and butane or combinations thereof and the combustion-supporting gas occurs in a conventional manner within blowpipe T, the mixture being thereafter discharged from the nozzle portion N of blowpipe T as preheat gas." The cutting gas, oxygen, is supplied to gas conduit 16 through a solenoid valve 22 for performing the actual cutting or metal-piercing operation.

Located directly below blowpipe T in close proximity to the stream of emerging gas is an automatic pilot igniter S which provides a pilot flame for igniting the preheat gas. Ignition gas is supplied to the pilot igniter S through a solenoid valve 24. The pilot flame is ignited by means of a spark developed from a spark plug or other high-voltage means encased within the igniter S. It is also possible to ignite the preheat gas directly from a spark rather than a pilot flame.

In carrying out the present invention, the distance between the outlet end of nozzle N and the pilot igniter S is not critical, although for practical reasons a distance of 2 to 4 inches is preferred.

Referring now-to FIGv 2 in which is shown a sequential timing diagram of a complete operating cycle. A complete operating period, i.e. when the torch is initially lit to where it is turned off, is depicted in FIG. 2(a The ignition period is shown in FIG. 2(b The preheat time period shown in FIG. 2(c begins at the termination of the ignition period. The actual cutting time which extends for the greater portion of the operating period is shown in FIG. 2(d The preheat solenoid valves are turned on and off during the ignition period to effect pulsing of the preheat gas as shown in FIG. 2(e The average preheat gas velocity is controlled by the ratio of off time to on time for solenoid valves 18 and 20 during the ignition period in the manner to be described in connection with the system of FIG. 3.

FIG. 3 shows the preferred system for pulsing the preheat gas. In this system solenoid valves 18 and 20 are placed in series with conventional switching means 26 and 28 which are preferably solid-state devices such as triacs. When the switching means 26 and 28 are turned on" solenoid valves 18 and 20 are activated supplying fuel gas and combustion-supporting gas, respectively, to torch T where the gases are appropriately mixed and discharged through nozzle N as preheat gas.

In the present operation switching means 26 and 28 are maintained on by the output of amplifier 30 throughout the preheat and cutting periods and are simultaneously turned on and off throughout the ignition period. Any conventional circuit means may be used to pulse switching means 26 and 28 during the initial ignition period. One way to accomplish this is by means of a conventional relaxation oscillator 32, the output pulse frequency of which is controllable. Each generated output pulse is fed to amplifier 30 to reverse bias the amplifier, i.e. turn it off for a predetermined period of time. Hence, solenoid valves 18 and 20 are intermittently interrupted for producing a pulsed gas flow. The input signal to relaxation oscillator 32 is applied only during the ignition period and may represent the same ignition signal applied to the pilot igniter S. Power is supplied to the system from a common power supply Set forth below is a typical example illustrating the required off-on time for the preheat solenoids l8 and 20 necessary to establish a stable self-sustaining flame where:

Fuel gas =natural gas Preheat velocity =500 f.p.s.

Rate of flame propagation =50 f.p.s.

Repetitive during ignition period: Off time: 1.35 see;

on time=.05 see. g M p M Offtime" to on time ratio 2711 The exit gas velocity during the ignition period falls to an effective average exit velocity which is low enough to maintain a stable self-sustaining flame without the occurrence of flashback.

The off-on time ratio may be maintained constant if the preheat velocity as given in the example above is not to exceed 500 f.p.s. However, it is preferred to provide the operator with a variable control so that he may vary the ratio for optimum performance for any given preheat velocity. In the system shown in FIG. 3 the relaxation oscillator circuit is designed such that the off time can be varied in the range from about 2 seconds down to about 0.05 seconds and the on time increased from about 0.05 seconds to about 0.3 seconds.

What we claim is: I

l. A method of establishing a self-sustaining high-velocity oxyfuel preheat gas flame for treating a metal surface which comprises: discharging preheat gas at a velocity of at least feet per second from a blowpipe, said preheat gas consisting of a predetermined mixture of fuel gas and a combustion-supporting gas; igniting said high-velocity preheat gas for an ignition period to form a preheat flame, and pulsating the flow of preheat gas during said ignition period such that the preheat gas flame is repetitively turned off for a time period of between 2 to 0.5 seconds and back on for a time period of between 0.05 to 0.3 seconds, whereby a self-sustaining preheat flame is established after said ignition period has terminated.

2. A method as defined in claim 1 wherein the preheat gas comprises a mixture of a fuel gas selected from the'class consisting of natural gas, propane, methane and butane and a combustion-supporting gas. 

1. A method of establishing a self-sustaining high-velocity oxyfuel preheat gas flame for treating a metal surface which comprises: discharging preheat gas at a velocity of at least 100 feet per second from a blowpipe, said preheat gas consisting of a predetermined mixture of fuel gas and a combustion-supporting gas; igniting said high-velocity preheat gas for an ignition period to form a preheat flame, and pulsating the flow of preheat gas during said ignition period such that the preheat gas flame is repetitively turned off for a time period of between 2 to 0.5 seconds and back on for a time period of between 0.05 to 0.3 seconds, whereby a self-sustaining preheat flame is established after said ignition period has terminated.
 2. A method as defined in claim 1 wherein the preheat gas comprises a mixture of a fuel gas selected from the class consisting of natural gas, propane, methane and butane and a combustion-supporting gas. 